ASTRONOMICAL NOTES.

Press, Volume LVII, Issue 17315, 29 November 1921, Page 9

ASTRONOMICAL NOTES.

FOR DECEMBER. (SPErUI.LT WBITTEN FOR "THE PRESS.' ) (By E. G. Hogg, M.A., F.R.A.S.) The sun enters the zodiacal signCapricornus on .December 22nd at 8.3S p.m., when the soKtico occurs: the sun on this dav reaches ; ts greatest altitude in Iho sky which for the latitude of Clirivtchureh is 69deg. 57mins.; the earth's diV.anr© from the sun on this dr.to will be about 91,220,000 miles. The sun will rise on Derember 22nd at 4-19 a.m. and <"fc at 7.39 p.m., an interval of 15h. 20i:,. as against Bh. 51 in. on Juiio 2'2ud, the shortest day in the Souther;' Hemisphere.

The planet Mercury will rise on Decomber Ist at 3.42 a.m. and on the loth at 3.51 a.m.; Venus rises on these dates at 3-63 a.m. and 3.32 a.m. respectively. Mars rises on December Ist at 1.59 a.m. and or. December loth at 1.23 a.m. Jupiter rises on these dates at 1.52 a.m. Jupiter rises on these dates at 1.52 a.m. and 1.2 a.m. respectively, and Saturn at 1.41 a.m. and 12.49 B.m. respectively. At the beginning of the month the five planets r.bovc-named will all bo visible in the eastern fky shortly "before dawn, but as the month prepresses Mercury will rapidly approach the sun and cease to be visible. All the planets will be conspicuous objects except Mars, which will be only slightly brighter than a second magnitude ,; ar . The distances in miles of the planets from th e earth on December Ist am as follows: —Mercury 120,034,000, Venus 149.320,000, Mars 189,P?0 O00! Jupiter 5-32,140.000, Saturn 929,3-10.000. Aii occultation of the planet Jupiter bv the moon takes place on December 23rd, but as conjunction between the two bodies does not occur until 1.25 p.m. it will be necessary to use a telescope to view the phenomenon. The moon rises on this day at 12.8 a.m. and Jupiter at 12.33 a.m., hence when the latter is ab&ye the horizon the two will appear to be about 6 deg. apart; during the day the moon will move forward in its orbit about 13 degrees, while the planet will only advance about 7mins. of arc hence as the morning passes the moon will gradually catch th e planet up ?nd finally hide it from view for a time. On the following dav there will be an occultation of the .planet Mars by the moon, oonj'inotion taking place at 10.29 ■ am.; in the latitude of Christchurch tho planet will jusi escape being eclipsed, but in the "North Island a brief occultation should occur. Soma coming scientific events cast long shadows beforo them. The total eon'rise of the <sun on September 20th, 1922., i* one or " these. t The, New Zealand Astronomical Society is already .enquiring if any of its members wish to take advantage of the offer made -'.bj the Commonwealth Government to \ transport observers and their equip- > jnenfc in one of the vessels of their navy "•to Wallal, on tho north-west coast nf -'.-■, Australia, one of the best sites avajl- ' .fthle for observing the phenomenon. ;!The. main interest of this and other expeditions to see the eelinse centres in Hhe' attempt which will be made to ; v ;'verify the conclusions deduced from the observations made at the total eclipse of- May 29th, 1910, that a wave of light,; from a star is slightly deflected from* its'rectilinear path if it passes :lose to a largo gravitating mass like I (llie sun. The results then obtained 'ji. \ re-re not absolutely conclusive, and it ;i: ij to be hoped that the present expedi--1; tion, profiting by. the experience gained | on"that occaaionj will settle the ques- '-;, tion decisively...; . . :■. - the-jearth's sur-r ' objured the east coast of , Ambfy-jusfc norta of the.Equator,, pass•:jfe^vef■ the Indian Ocean, and enters • 4 NjotthWest Australia at "Wallal, in :'>lalitu6!e 20 degrees south. After Central Australia; it leaves continent in Sontii-East be located somewhere on band, as it is oniy when the sun's ffpht-is entirely cut off that the stars fl|TOg: nearly in tne ne 111™, sun can be photographed, and the iMWinges-apparently made in their rela||Pf&;J>ositionß by tihe sun's gravitational l|iij§j&!* can be defected. The choice of is no easy matter, owing of. conditions which have }t results of a high order to be attained. It is very SdlSffablei "that Ihe pajriod of totality |||uould be as long as possible, that at St Si'instant of eclipse the sun should in the heavens, and that there. stMntrald he a reasonable probability of fp6«icl weather when tho supreme moment ig'amves.' '.-■■ •||Pl???' ;cohditions quite well," as the iJWJ'of'toteKtjf there is smin 18sec. altitude is 58 degrees, and rainfall for September and for some years past has not inches per month, while of cloudiness is said to jmd iihe wind light. Wallal, to be somewhat diffithere being apparently s^iM|* 0 9 n r..or pier of any dfiscription. I^^^VearTOrs /having been conveyed ad as is safe, can only beaching their boats with i^W^io^, or trusting to the local surfhence'"any heavy equipment is of question. Once landed go happily, as there is a well with abundance\ of wafer, and .trees in whose midst

the camp can be established; and as the country round is desert, the observers will find little to distract their attention from the work before them, it is much to be hoped that from among the astronomical enthusiasts of INew Zealand some will be found to make the trip, and it may be some inducement to them to go to learn that the Lick Observatory has definitely wii i to send an ex I )editiou *°

It may be asked whv do our obse"'crs. not select a site in Queensland which is so much nearer to our shores? inc. reason-, which have decided the iScw Zealand Astronomical Society to leave Queensland out of ' their "programme are probably the same as thosa which have made the special committee or tli e American Astronomical Kocietv appointed tT enquire as to sites for an expedition i 0 fight shy of the eastern «pa-boari of Australia. This committee has examined three noiaible sites in Queensland, all comparatively easy of access, but finds that in each case the period of totality is rather short, that the sun is low at the time of the eclipse : that eood weather cannot he linpofull.v predicted and that there is a prevalence of dust-storms which misdit prove highly disconcerting if occurring at thf. time of the eclipse. Under these circumstances the committee reports that it is unable to recommend that technical observers of the e-lipse :hnu!d seriously consider a location in Queensland. It may be addc l that th* Eclipse Committee of the Royal Society of London and Royal Astronomical Society ar e going to pin their fnith to Christmas Island which lies along the track of totality; their observers are being sent there several months in advance of th 0 eclipse date so that th-\v may obtain night photographs of the srtars which will become visibTo during the eclipse with the instruments which will be usetf in their observations in September next. The chances of suitable weather conditions at Christmas Island, however, do not seem as good as those at AVallal. but the sun will be at a splendid altitude for observation and the period of totality good though shorter than at Wallal. Thero is no more striking constellation in our winter skies than the Scorpion which moves through the. heavens like a gigantio note of interrogation: the mo3t star in this fine group is the ruby-red Antares, one of the four stars which primitive astronomers termed royal. From a note in a recent issue of "Nature" it appears that Mr F. G. Pease, working -with the 100-inch Hooker telescope at Mt. Wilson, has succeeded, in measuring its angular diameter, which ho finds to be .04 seconds of arc, a result practically identical with that (;043) predicted by Professor Eddington on physical grounds. The parallax of Antares is rather doubtful but taking the most probable value .009 seconds of arc, the liniar diameter of the star is no less than 400,000,000 miles—a quantity greatly transcending in magnitude that obtained in the case of Betelguese—27o million miles—as described in these notes for May last. One of the most important conclusions reached in modern stellar astronomy is that though stars may differ enormously in size and brightness, the limits between which their masses lie are comparatively close; if the diameter of Antares given above is correct, this star has a volume about 100 million times that of our sun, but it is extremely improbable that its mass is more than one hundred times that of our sun. The tenuity of th e gases of which this star is composed quite baffles our imagination; it is very difficult indeed to understand how the star's spectrum can be reconciled with the low density which the star appears to possess and it is probable that in the lighiw of further knowledge Borne of the results obtained in the case of Antares. and Betelguese will be considerably modified.,

Antares is attended by a quaint companion which jt exceeds in brightness by about .6 magnitudes; the two are separated by about 3.2 seconds of arc, or, using the parallax assumed above, by about 2100 million miles. Though the two have been under observation for over 70 years, no change has been noted in their relative positions, but as they possess a common proper motion it is inferred that they are physically connected. Iri an orbit of dimensions such as we have in this case, we should ejjpeot the two bodies to move very slowly round their common centre of gravity, and it may be that centuries will elapse before any measurable change of position will he noted. An account of an exceptionally high solar prominence observed at the Tories Observatory on October Bth, 1920, is quoted in .a recent issue of the "Astrophysical Journal"; it was not associated with any sun-spot, and, there was no evidence of any particular disturbance in this region of the sun's surface beyond a few floccular specks. The measures of the upward velocity of portions-of the prominence which were obtained show that the speed of ascent- was subject to the remarkable sudden increases which appear to be characteristic of the motions of all iarge prominences. The superstructure rose slowly at first, until coherence with the base was partly broken, when the velocity changed instantly to a much higher value which persisted until a more complete break took place, with another sudden increase of speed. The prominence w*s followed until it died away at the record height of 520:000 miles from *he solar surface. No explanation is at present forthcoming as to the cause of these peculiar variations- in speed of the matter carried outward in the development and v subsequent decay of a tvrominence; though thev are probably electrostatic effects, there is no agreement among solar physicists as to the iheclv:n''sm by means of which they are carried out.